In recent years, novel devices that utilize the charges of electrons and the nature of spins at the same time have been actively studied. In a spin transistor that is one of such novel devices, a magnetic material is used as a source electrode and a drain electrode, and output characteristics can be controlled by changing the relative magnetization directions of the source electrode and the drain electrode. That is, this control is performed by taking advantage of the fact that the drain current (IDP) increases when the relative magnetization directions of the source electrode and the drain electrode are substantially parallel, and the drain current (IDAP) decreases when the relative magnetization directions are substantially antiparallel. When a spin transistor is used in a memory or a reconfigurable logic circuit, the IDP/IDAP ratio or the drain current difference between a substantially parallel magnetization state and a substantially antiparallel magnetization state needs to be increased. To increase the IDP/IDAP ratio, the spin polarization rate of the magnetic material used as the source electrode and the drain electrode needs to be increased. However, even if a magnetic material with a spin polarization rate of 100% is used, the IDP/IDAP ratio becomes lower when a finite bias is applied between the source electrode and the drain electrode. Also, the characteristics indicating the current equal to or lower than the threshold value (the subthreshold swing value (the S value)) cannot become lower than 60 mV/decade in theory, which hinders a power consumption reduction in the circuit.
As described above, when a finite bias is applied between the source electrode and the drain electrode, the IDP/IDAP ratio of the spin transistor becomes lower, and the S value cannot become lower than 60 mV/decade.